Make Kopia file parallelism configurable

[qiuming-best]

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Please add a summary of your change

Implementation of #7005

• Add one generic API struct for the configuration of the Uploader
• Add ParallelFilesUpload configuration for Kopia UploadPolicy

Does your change fix a particular issue?

Fixes #(issue)
#6607

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file or added /kind changelog-not-required as a comment on this pull request.
• Updated the corresponding documentation in site/content/docs/main.

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (5c958d8) 61.68% compared to head (c2d4495) 61.69%.

Files	Patch %	Lines
pkg/cmd/util/output/backup_describer.go	42.85%	4 Missing ⚠️
pkg/uploader/provider/restic.go	0.00%	2 Missing and 1 partial ⚠️
pkg/controller/data_upload_controller.go	0.00%	0 Missing and 1 partial ⚠️
pkg/controller/pod_volume_backup_controller.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7000   +/-   ##
=======================================
  Coverage   61.68%   61.69%           
=======================================
  Files         258      258           
  Lines       27613    27636   +23     
=======================================
+ Hits        17034    17050   +16     
- Misses       9387     9393    +6     
- Partials     1192     1193    +1     

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[anshulahuja98]

Sorry for a late comment, didn't get a chance to review the design.
just wondering if we evaluated between passing this value as part of backup/restore API vs making it a server setting?
Any rationales around this.
From my thinking, a user might not really wish to use different uploaderconfig for each backup and might just prefer to have it set once at server level. This might be sufficient for most use cases.

[qiuming-best]

@anshulahuja98
Thank you for your suggestion; we have internally discussed this matter. Due to the various configuration options in Velero, the placement of these configurations is relatively unclear. We believe that some configurations can be placed at the server level, while others are associated with backup or restore. To clearly define the location of configurations, we have decided to place configurations related to backup or restore in the respective Backup or Restore Custom Resource (CR). Currently, aspects such as concurrency control and upcoming tasks like Kopia Sparse and Ignore Folder parameters are all linked to specific backup or restore operations and will therefore be placed in the corresponding CRs. Of course, we will also consider how to better distinguish where these configurations should be placed in the future.

[navilg]

@Lyndon-Li @blackpiglet If we do not set this value/flag during backup/schedule creation, What will be default value of parallel files upload ? I tried to find it, didn't find anywhere in doc.

Also if there is any document you can point me to about difference between node-agent concurrency and parallel files upload.

Thanks

[blackpiglet]

@navilg
By default, it should be 0, meaning the parallel set is not enabled.

[navilg]

Ohkay. Does parallel set value 1 means two files can be uploaded at a time ?

[blackpiglet]

AFAIK, 1 means only one parallel. 2 means two files can be uploaded concurrently.